+/**
+ * Determine if a meta key is set for a given object
+ *
+ * @since 3.3.0
+ *
+ * @param string $meta_type Type of object metadata is for (e.g., comment, post, or user)
+ * @param int $object_id ID of the object metadata is for
+ * @param string $meta_key Metadata key.
+ * @return boolean true of the key is set, false if not.
+ */
+function metadata_exists( $meta_type, $object_id, $meta_key ) {
+ if ( ! $meta_type )
+ return false;
+
+ if ( ! $object_id = absint( $object_id ) )
+ return false;
+
+ $check = apply_filters( "get_{$meta_type}_metadata", null, $object_id, $meta_key, true );
+ if ( null !== $check )
+ return true;
+
+ $meta_cache = wp_cache_get( $object_id, $meta_type . '_meta' );
+
+ if ( !$meta_cache ) {
+ $meta_cache = update_meta_cache( $meta_type, array( $object_id ) );
+ $meta_cache = $meta_cache[$object_id];
+ }
+
+ if ( isset( $meta_cache[ $meta_key ] ) )
+ return true;
+
+ return false;
+}
+
+/**
+ * Get meta data by meta ID
+ *
+ * @since 3.3.0
+ *
+ * @param string $meta_type Type of object metadata is for (e.g., comment, post, or user)
+ * @param int $meta_id ID for a specific meta row
+ * @return object Meta object or false.
+ */
+function get_metadata_by_mid( $meta_type, $meta_id ) {
+ global $wpdb;
+
+ if ( ! $meta_type )
+ return false;
+
+ if ( !$meta_id = absint( $meta_id ) )
+ return false;
+
+ if ( ! $table = _get_meta_table($meta_type) )
+ return false;
+
+ $id_column = ( 'user' == $meta_type ) ? 'umeta_id' : 'meta_id';
+
+ $meta = $wpdb->get_row( $wpdb->prepare( "SELECT * FROM $table WHERE $id_column = %d", $meta_id ) );
+
+ if ( empty( $meta ) )
+ return false;
+
+ if ( isset( $meta->meta_value ) )
+ $meta->meta_value = maybe_unserialize( $meta->meta_value );
+
+ return $meta;
+}
+
+/**
+ * Update meta data by meta ID
+ *
+ * @since 3.3.0
+ *
+ * @uses get_metadata_by_mid() Calls get_metadata_by_mid() to fetch the meta key, value
+ * and object_id of the given meta_id.
+ *
+ * @param string $meta_type Type of object metadata is for (e.g., comment, post, or user)
+ * @param int $meta_id ID for a specific meta row
+ * @param string $meta_value Metadata value
+ * @param string $meta_key Optional, you can provide a meta key to update it
+ * @return bool True on successful update, false on failure.
+ */
+function update_metadata_by_mid( $meta_type, $meta_id, $meta_value, $meta_key = false ) {
+ global $wpdb;
+
+ // Make sure everything is valid.
+ if ( ! $meta_type )
+ return false;
+
+ if ( ! $meta_id = absint( $meta_id ) )
+ return false;
+
+ if ( ! $table = _get_meta_table( $meta_type ) )
+ return false;
+
+ $column = esc_sql($meta_type . '_id');
+ $id_column = 'user' == $meta_type ? 'umeta_id' : 'meta_id';
+
+ // Fetch the meta and go on if it's found.
+ if ( $meta = get_metadata_by_mid( $meta_type, $meta_id ) ) {
+ $original_key = $meta->meta_key;
+ $original_value = $meta->meta_value;
+ $object_id = $meta->{$column};
+
+ // If a new meta_key (last parameter) was specified, change the meta key,
+ // otherwise use the original key in the update statement.
+ if ( false === $meta_key ) {
+ $meta_key = $original_key;
+ } elseif ( ! is_string( $meta_key ) ) {
+ return false;
+ }
+
+ // Sanitize the meta
+ $_meta_value = $meta_value;
+ $meta_value = sanitize_meta( $meta_key, $meta_value, $meta_type );
+ $meta_value = maybe_serialize( $meta_value );
+
+ // Format the data query arguments.
+ $data = array(
+ 'meta_key' => $meta_key,
+ 'meta_value' => $meta_value
+ );
+
+ // Format the where query arguments.
+ $where = array();
+ $where[$id_column] = $meta_id;
+
+ do_action( "update_{$meta_type}_meta", $meta_id, $object_id, $meta_key, $_meta_value );
+
+ if ( 'post' == $meta_type )
+ do_action( 'update_postmeta', $meta_id, $object_id, $meta_key, $meta_value );
+
+ // Run the update query, all fields in $data are %s, $where is a %d.
+ $result = (bool) $wpdb->update( $table, $data, $where, '%s', '%d' );
+
+ // Clear the caches.
+ wp_cache_delete($object_id, $meta_type . '_meta');
+
+ do_action( "updated_{$meta_type}_meta", $meta_id, $object_id, $meta_key, $_meta_value );
+
+ if ( 'post' == $meta_type )
+ do_action( 'updated_postmeta', $meta_id, $object_id, $meta_key, $meta_value );
+
+ return $result;
+ }
+
+ // And if the meta was not found.
+ return false;
+}
+
+/**
+ * Delete meta data by meta ID
+ *
+ * @since 3.3.0
+ *
+ * @uses get_metadata_by_mid() Calls get_metadata_by_mid() to fetch the meta key, value
+ * and object_id of the given meta_id.
+ *
+ * @param string $meta_type Type of object metadata is for (e.g., comment, post, or user)
+ * @param int $meta_id ID for a specific meta row
+ * @return bool True on successful delete, false on failure.
+ */
+function delete_metadata_by_mid( $meta_type, $meta_id ) {
+ global $wpdb;
+
+ // Make sure everything is valid.
+ if ( ! $meta_type )
+ return false;
+
+ if ( ! $meta_id = absint( $meta_id ) )
+ return false;
+
+ if ( ! $table = _get_meta_table( $meta_type ) )
+ return false;
+
+ // object and id columns
+ $column = esc_sql($meta_type . '_id');
+ $id_column = 'user' == $meta_type ? 'umeta_id' : 'meta_id';
+
+ // Fetch the meta and go on if it's found.
+ if ( $meta = get_metadata_by_mid( $meta_type, $meta_id ) ) {
+ $object_id = $meta->{$column};
+
+ do_action( "delete_{$meta_type}_meta", (array) $meta_id, $object_id, $meta->meta_key, $meta->meta_value );
+
+ // Old-style action.
+ if ( 'post' == $meta_type || 'comment' == $meta_type )
+ do_action( "delete_{$meta_type}meta", $meta_id );
+
+ // Run the query, will return true if deleted, false otherwise
+ $result = (bool) $wpdb->delete( $table, array( $id_column => $meta_id ) );
+
+ // Clear the caches.
+ wp_cache_delete($object_id, $meta_type . '_meta');
+
+ do_action( "deleted_{$meta_type}_meta", (array) $meta_id, $object_id, $meta->meta_key, $meta->meta_value );
+
+ // Old-style action.
+ if ( 'post' == $meta_type || 'comment' == $meta_type )
+ do_action( "deleted_{$meta_type}meta", $meta_id );
+
+ return $result;
+
+ }
+
+ // Meta id was not found.
+ return false;
+}
+
+/**
+ * Update the metadata cache for the specified objects.
+ *
+ * @since 2.9.0
+ * @uses $wpdb WordPress database object for queries.
+ *
+ * @param string $meta_type Type of object metadata is for (e.g., comment, post, or user)
+ * @param int|array $object_ids array or comma delimited list of object IDs to update cache for
+ * @return mixed Metadata cache for the specified objects, or false on failure.
+ */